Transflective liquid crystal display apparatus

ABSTRACT

To provide a transflective liquid crystal display apparatus that employs in-plane switching mode (in-plane switching system), which exhibits a reflection property of wide view angles. Provided is a transflective liquid crystal display apparatus which comprises: a reflective area and a transmissive area; an uneven reflective plate provided in the reflective area; a flattening film laminated on the uneven reflective plate; and common electrodes and pixel electrodes arranged on the flattening film, wherein, the uneven reflective plate comprises a diffusive reflecting function that is capable of diffusely reflecting light making incident at an incident angle of 30 degrees towards directions at exit angles of 0-10 degrees, and a surface of the flattening film is set to be substantially flat.

The preset application is a continuation of U.S. application Ser. No.11/756,513 filed May 31, 2007, which claims priority to Japanese PatentApplication No. 2006-155449 filed on Jun. 2, 2006. The entire disclosureof the prior applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transflective liquid crystal displayapparatus and, more specifically, to a transflective liquid crystaldisplay apparatus in which each pixel comprises a light-reflection typereflective area and a light-transmission type transmissive area.

2. Description of the Related Art

FIG. 10 illustrates a conventional case depicted in Japanese UnexaminedPatent Publication 2003-344837 (Patent Literature 1). A liquid crystaldisplay apparatus 100 shown in FIG. 10 is constituted with a lower sidesubstrate 11, a counter side substrate 12, and a liquid crystal layer 13held by being interposed therebetween. Further, each of the pixelsconstituting the display unit of the liquid crystal display apparatus100 comprises a light-reflection type reflective area and alight-transmission type transmissive area. FIG. 10 shows a schematicsectional view of a single pixel that is disclosed in Patent Literature1.

In FIG. 10, the counter side substrate 12 is constituted with a blackmatrix layer 17 formed on a transparent insulating substrate 22 b as alight-shielding film, a color layer 18 that is partially overlapped withthe black matrix layer 17, and a transparent overcoat layer 19 formed onthe black matrix layer 17 and the color layer 18. Further, in order toprevent the liquid crystal layer 13 from being electrically influencedby the electrification from the surface of a liquid crystal displaypanel generated due to a contact or the like, a transparent conductivelayer 15 is formed on the back face of the transparent insulatingsubstrate 22 b. The color layer 18 is formed with a resin filmcontaining dyes or pigments of red (R), green (G), and blue (B).

Further, the lower side substrate 11 comprises: on a transparentinsulating substrate 22 a, a first metal layer where scanning lines (notshown) and gate electrodes (not shown) of thin film transistors used fordriving are formed; a first interlayer insulating film 23 formedthereon; a second metal layer formed on the first interlayer insulatingfilm 23, on which data lines 24, source electrodes and drain electrodes(not shown) of the thin film transistors are formed; a second interlayerinsulating film 25 formed thereon; and common electrodes 26 and pixelelectrodes 27 formed thereon with transparent electrodes.

The lower side substrate 11 and the counter side substrate 12respectively comprise an alignment film 20 a and an alignment film 20 bon the respective opposing face sides thereof. Rubbing processing isapplied thereon from the extending direction of the pixel electrode 27and the common electrode 26 towards a prescribed direction tilted byabout 10 to 30 degrees so that the liquid crystal layer 13 is alignedhomogeneously. Thereafter, both substrates are laminated to face eachother. This angle is called an initial alignment direction of the liquidcrystal molecules.

A spacer (not shown) is provided between the lower side substrate 11 andthe counter side substrate 12 for keeping the thickness of the liquidcrystal layer 13. Further, a seal (not shown) is formed in the peripheryof the liquid crystal layer 13 for not leaking the liquid crystalmolecules to the outside.

In addition to the data lines 24 through which data signals aresupplied, common electrode wirings (not shown) and the common electrodes26 through which reference potential is supplied, and the pixelelectrodes 27 that correspond to the pixels to be displayed, the lowerside substrate 11 comprises scanning lines (not shown) through whichscanning signals are supplied and the above-mentioned driving thin filmtransistors (TFTs) (not shown) which are provided on the transparentinsulating substrate 22 a.

A driving thin film transistor comprises a gate electrode, a drainelectrode, and a source electrode, and it is provided by correspondingto each pixel in the vicinity of the intersection between the scanningline and the data line 24. The gate electrode is electrically connectedto the scanning line, the drain electrode to the data line 24, and thesource electrode to the pixel electrode 27.

The common electrode 26 and the pixel electrode 27 are both in apectinate shape, and the teeth of each electrode are all extended inparallel to the data line 24. Furthermore, the teeth of the commonelectrode 26 and that of the pixel electrode 27 are arranged alternatelywith each other.

An in-plane switching system is employed for both of the above-mentionedtransmissive area T and reflective area H of the liquid crystal displayapparatus 100. Regarding the liquid crystal display apparatus 100, inthe pixel to which the data signals (selected by the scanning signalssupplied through the scanning lines, and supplied through the data lines24) are written, parallel electric fields are generated in theabove-described transparent insulating substrates 22 a, 22 b between thecommon electrodes 26 and the pixel electrodes 27. The alignmentdirection of the liquid crystal molecules is rotated within a plane inparallel to the transparent insulating substrates 22 a, 22 b inaccordance with the generated electric field so as to perform aprescribed display.

A vertically long area surrounded by the above-described commonelectrode 26 and the pixel electrode 27 is called a column (not shown).In the above-described liquid crystal display apparatus 100, the commonelectrode 26 and the pixel electrode 27 are both formed with atransparent material, indium tin oxide (ITO).

Further, in the transmissive area T and the reflective area H, thecommon electrode 26 is formed on a layer that is closer to the liquidcrystal layer than to the scanning line and the data line 24, and it isformed to have a wider width than the scanning line and the data line 24so as to cover the scanning line and the data line 24 completely.

Furthermore, as shown in FIG. 10, in the reflective area H, a reflectiveplate 9 is formed on a layer that is closer to the liquid crystal layerthan to the scanning line and the data line 24, and it is disposed tocover the scanning line and the data line 24 completely.

By forming the common electrode 26 and the reflective plate 9 in thismanner, it is possible to shut the leaked electric field from the dataline 24 and the scanning line. Thus, the effective display area that canbe controlled by the electric field generated between the pixelelectrode 27 and the common electrode 26 can be expanded. Therefore, theaperture ratio can be improved.

Furthermore, as can be seen from FIG. 10, the second interlayerinsulating film 25 is provided between the common electrode 26 and thedata line 24 in the transmissive area T.

Through setting the ratio d/ε of the film thickness (d) with respect tothe permittivity (ε) of the second interlayer insulating film 25sufficiently large, the parasitic capacitance between the data line 24and the common electrode 26 can be decreased. Further, as can be seenclearly from FIG. 10, in the reflective area H, the second interlayerinsulating film 25, a second insulating film 8 b, the reflective plate9, and a third insulating film 8 c are provided between the commonelectrode 26 and the data line 24. This provides a proper distancebetween the data line 24 and the common electrode 26, thereby decreasingthe parasitic capacitance.

In this conventional case, the common electrode 26 and the pixelelectrode 27 are both formed on the second interlayer insulating film 25in the transmissive area T, and the common electrode 26 and the pixelelectrode 27 are both formed on the third insulating film 8 c in thereflective area H. Therefore, the common electrode 26 and the pixelelectrode 27 can be formed by the same step and the same material, whichimproves the manufacture efficiency.

Further, after forming the interlayer insulating film 25, a secondinsulating film 8 b is formed in the reflective area H. The secondinsulating film 8 b is normally formed with a double-layer structureconstituted with an uneven film and a flattening layer. However, it canalso be formed with a single-layer structure by using a halftone mask.

Furthermore, the reflective plate 9 made of aluminum is formed on thesecond insulating film 8 b whose surface is uneven. This reflectiveplate 9 functions to reflect the incident light diffusely. The thirdinsulating film 8 c is formed over the reflective plate 9 and thesurface thereof is flattened. Further, the common electrode 26 and thepixel electrode 27 made of indium tin oxide (ITO) as in the case of thetransmissive area T are formed on the third insulating film 8 c, and analignment film 20 a is formed thereon to constitute the lower sidesubstrate 11.

In the above-described conventional case shown in FIG. 10, a thinflattening film is provided on the uneven reflective plate 9 in thereflective area H, and interdigital electrodes are provided thereon.Meanwhile, the transmissive area T has a structure where theinterdigital electrodes of the same layer as that of the reflectiveinterdigital electrodes are directly formed on the second interlayerfilm (without providing the uneven layer and the flattening layer).

There is a difference in heights provided between the transmissive partand the reflective part (reflective part-transmissive part difference)by the difference of “uneven layer+reflective part metal+flatteninglayer” to provide a prescribed retardation (phase difference between twokinds of intrinsic polarization light) between the reflective part (Δnd(R)) and the transmissive part (Δnd (T)) by that difference.

The refractive index anisotropy of the liquid crystal (Δn) is aboutΔn=0.1. Thus, provided that Δnd (T)−Δnd(R)=(λ/2)−(λ/4)=137 nm, it isnecessary to provide the reflective part-transmissive part difference ofabout 1.3 μm. In this case, about 0.1-0.3 μm is required for the filmthickness of the reflective part metal (aluminum), so that the thicknessof the “uneven layer+flattening layer” becomes about 1.0 μm.

Further, in the above-described conventional case, there is norestriction set in the reflection mode regarding the angle of theincident light and the angle of the exit light with respect to theliquid crystal.

The angle of the incident light and the angle of the emitted light withrespect to the liquid crystal at the time of the reflection mode in theabove-described conventional case will be investigated herein.

In the above-described conventional case, the in-plane switching systemis employed for driving the liquid crystal. In this drive method, it isnecessary to set the pretilt angle of the liquid crystal to be close to5 degrees or less (preferably 0 degree) as much as possible.

This is because of the following reasons. That is, if the pretilt of theliquid crystal is too large, idealistic in-plane switching drive cannotbe performed and there generates alignment disturbances, since theliquid crystal keeps the pretilt to be aligned in a tilted manner on thesubstrate surface. Therefore, contrast and the viewing angle aredeteriorated, thereby deteriorating the display quality.

Now, the relation regarding the settings of the above-described tiltangle of the unevenness, the incident angle, the exit angle, and theoperation of the entire apparatus will be analyzed further.

When the incident angle of the light is as shallow as 0-15 degrees andthe exit angle is 0 degree, the tilt angle of the uneven reflectiveplate can be set as shallow, and the film thickness of the unevennessmay be set as about 0.5 μm. For easing the difference in the heights ofthe uneven parts, it is necessary to provide a flattening film havingthe thickness about the same as that of the uneven film. Thus, thethickness of the flattening film also needs to be about 0.5 μm.

When the tilt angle of the uneven reflective plate is gentle as in thiscase, the rise and fall of the uneven parts on the surface of theflattening film under the interdigital electrodes is relatively gentleeven if the uneven film or the flattening film is thin, and the patternformation of the interdigital electrodes is relatively easy. Further,there causes no disturbance even when the liquid crystal is driven inthe lateral electric field, and there is not much deteriorationgenerated in the display quality mentioned above.

In the meantime, when the incident angle of the light is as deep as30-15 degrees and the exit angle is 0 degree, and the tilt angle of theuneven reflective plate is deep, it is necessary to thicken the unevenfilm. In this case, the difference between the uneven parts on thesurface of the flattening film under the interdigital electrodes becomesalso significant depending on the material and the thickness of theflattening film. Therefore, the pattern formation of the interdigitalelectrodes becomes difficult. Further, there often causes disturbance inthe liquid crystal when the liquid crystal is driven in the lateralelectric field, which often results in causing deterioration of thecontrast and the viewing angle. Therefore, it is necessary in such acase to form the flattening film to be thick.

As described above, when a priority is given to the flatteningcharacteristic under the interdigital electrodes in the reflective area,the uneven film and the flattening film both become thick. Thus, in thestructure of the above-described conventional case, it is difficult toset the reflective part-transmissive part difference to be about 1.0 μm,for example. Therefore, in the conventional transflective liquid crystaldisplay apparatus of an In-plane switching mode, it is difficult toobtain the reflective characteristic of wide view angles.

SUMMARY OF THE INVENTION

The object of the present invention therefore is to improve theinconveniences of the conventional case, and to provide a transflectiveliquid crystal display apparatus of an in-plane switching mode (in-planeswitching system), which has a reflection property of wide view angles.

In order to achieve the aforementioned object, each single pixelconstituting a transflective liquid crystal display apparatus accordingto the present invention comprises: a reflective area and a transmissivearea; an uneven reflective plate provided in the reflective area; aflattening film laminated on the uneven reflective plate; and commonelectrodes and pixel electrodes arranged on the flattening film,wherein, the uneven reflective plate comprises a diffusive reflectingfunction that is capable of diffusely reflecting light making incidentat an incident angle of 30 degrees towards directions at exit angles of0-10 degrees, and a surface of the flattening film is set to be flat orclose to flat.

Therefore, the driving electrodes can be attached/formed stably on theflattening film, so that it is possible to achieve the effect ofproviding the reflection property of wide view angles and improving thedurability of the entire apparatus.

The transflective liquid crystal display apparatus may be structuredsuch that, as a drive system for the liquid crystal, in-plane switching(IPS) mode or field fringe switching (FFS) mode is employed for both thereflective area and the transmissive area.

Further, an average tilt angle of the above-described uneven reflectiveplate may be set as 3-12 degrees, and an average tilt angle of thesurface of the flattening film may be set to a value not exceeding arange of 3-5 degrees. With this, a liquid crystal display apparatuswhich provides stable operations and comprises the reflection propertyof wide view angles can be obtained.

The average tilt angle of the uneven reflective plate may be set as 6-9degrees, and the average tilt angle of the surface of the flatteningfilm may be set to a value not exceeding a range of 3-5 degrees.

This enables the diffusive reflection to be set in a more effectivestate and, at the same time, the uneven part of the flattening filmbecomes close to flat. Therefore, the above-described electrodes can bestably attached/formed on the flattening film.

Furthermore, the uneven reflective plate may have a difference of 0.6 μmor more in heights of uneven parts, and a difference in heights on thesurface of the flattening film may be 0.4 μm or less.

Moreover, Δnd of a liquid crystal layer of the reflective area may beset as about λ/4, and Δnd of a liquid crystal layer of the transmissivemay be set as about λ/2. Also, the flattening film may be formeduniformly from the reflective area to the transmissive areacontinuously.

The refractive index anisotropy Δn of the flattening film may be set as0.001 or less.

With this, it is possible to avoid deterioration of the contrast even ifa flattening film is provided in the transmissive area (transmissivepart). Therefore, an excellent state can be maintained.

In the transflective liquid crystal display apparatus according to thepresent invention where the transmissive part (transmissive area) T andthe reflective part (reflective area) H both employ the in-planeswitching drive, the average tilt angle of the uneven parts of theuneven reflective plate is set at 3-12 degrees, for example, to allowdispersion of exit angles. Thus, it is possible to obtain the reflectionproperty of wide view angles for diffusely reflecting the light form thedirection at an incident angle of 30 degrees towards directions at exitangles of 0-10 degrees. Further, the flattening film is provided on theuneven reflective plate to make the top face of the layer on which theelectrodes are formed to be flat or close to flat, so that the drivingelectrodes can be stably attached/formed. With this, it is possible toprovide the transflective liquid crystal display apparatus that iscapable of improving the reliability and the durability of the entireapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram for showing a mutual relationbetween electrodes and the wirings thereof on the base substrate side ofa transflective liquid crystal display apparatus according to anembodiment of the present invention;

FIG. 2 is a schematic sectional view of a pixel part taken along theline E-E′ of FIG. 1;

FIG. 3 illustrates sectional views taken along the line F-F′ and theline G-G′ of FIG. 1, in which FIG. 3A is a fragmentary sectional viewfor showing a transmissive part (transmissive area) taken along the lineF-F′ of FIG. 1, and FIG. 3B is a fragmentary sectional view for showinga reflective part (reflective area) taken along the line G-G′ of FIG. 1;

FIG. 4 is an illustration for describing the relation between the tiltangle of an uneven reflective plate of the embodiment disclosed in FIG.1 and the incident angle/exit angle of light;

FIG. 5 illustrates the relation regarding the tilt angle of theflattening film surface (applied over the uneven reflective plate)according to the embodiment disclosed in FIG. 1 and the electrode widthprovided on the flattening film surface, in which FIG. 5A is anillustration for describing the tilt angle of the uneven reflectiveplate, FIG. 5B is an illustration for describing the tilt angle of theflattening film surface, and FIG. 5C is a graph for showing the relationbetween the flattening film thickness and the average tile angle of theflattening film surface;

FIG. 6 illustrates the relation between the flattening film and the baseuneven film according to the embodiment disclosed in FIG. 1, in whichFIG. 6A shows the relation regarding the relative thicknesses of theflattening film and the base uneven film, and FIG. 6B shows the Δnddependency of the transmission light intensity;

FIG. 7 is an illustration for describing the difference in heights ofthe transmissive part (transmissive area) and the reflective part(reflective area) of the flattening film part of the embodimentdisclosed in FIG. 1;

FIG. 8 is an illustration for showing the relation between the pixelelectrodes and the common electrodes according to another embodiment;

FIG. 9 illustrates fragmentary sectional views for showing a part of thetransmissive part (transmissive area) and the reflective part(reflective area) of FIG. 8, in which FIG. 9A is a schematic fragmentarysectional view taken along the line C-C′ of FIG. 8, and FIG. 9B is aschematic fragmentary sectional view taken along the line D-D′ of FIG.8; and

FIG. 10 is a schematic fragmentary sectional view for showing the pixelpart of the transflective liquid crystal display apparatus according tothe conventional case.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinafter byreferring to FIG. 1-FIG. 7. The same reference numerals are applied tothe structural elements that are the same as those of the conventionalcase described above.

FIG. 1 is a plan view for showing the positional relation between eachof the electrodes that are arranged in a single pixel area of atransflective liquid crystal display apparatus (IPS mode) 101 accordingto the embodiment. As shown in FIG. 1, each pixel of the transflectiveliquid crystal display apparatus 101 is sectioned and specified intocorresponding ranges by data liens 24 and scanning lines 28 provided inmatrix over the entire display apparatus.

FIG. 2 shows a schematic fragmentary sectional view (sectional viewtaken along the line E-E′ of FIG. 1) of the sectioned single pixel.

In FIG. 1, a transmissive area T is provided in the upper half part ofthe illustration, and a reflective area H is provided in the lower halfpart thereof.

In FIG. 1 and FIG. 2, the transflective liquid crystal display apparatus101 is constituted with a lower substrate 1, a counter substrate 2, anda liquid crystal layer 3 held by being interposed therebetween.

Among those, each of the laminated part of the counter substrate 2 ismainly constituted with those having various functions for display, andit is constituted almost in the same manner as that of the conventionalcase (FIG. 10) described above. That is, in this counter substrate 2, ablack matrix layer as a light shielding film, a color layer that ispartially overlapped on the black matrix layer, a transparent overcoatlayer, and an alignment film are laminated in order towards the liquidcrystal side from the insulating transparent substrate. Furthermore, thecounter substrate 2 comprises a conductive film made of a transparentmaterial for eliminating the electrification that is generated due to acontact or the like, and a polarizing plate, which are laminated inorder on the outer face side (opposite side of the liquid crystal) ofthe transparent substrate. The entire structure of the counter substrate2 is constituted thereby. The aforementioned color layer is formed witha resin film that contains dyes or pigments of Red (R), green (G), andblue (B).

Further, each of the laminated part of the lower substrate 1 is mainlyconstituted with those having various functions for driving displaymembers, and there are provided scanning lines through which scanningsignals are supplied and the aforementioned driving thin filmtransistors (TFT) 30 on the transparent insulating substrate, inaddition to the data lines 24 through which data signals are supplied,common electrode wirings 26 a, 26 b and common electrodes 26 (26A, 26B)to which reference potential is supplied, and pixel electrodes 26A, 27Bthat correspond to the pixels to be displayed.

A driving thin film transistor 30 comprises a gate electrode, a drainelectrode 30 a, and a source electrode 30 b, and it is provided by beingcorresponded to each pixel in the vicinity of the intersection betweenthe scanning line 28 and the data line 24. The gate electrode of thethin film transistor 30 is electrically connected to the scanning line28, the drain electrode 30 a to the data line 24, and the sourceelectrode 30 b to the pixel electrodes 27A and 27B.

The lower substrate 1 comprises, on the above-described transparentinsulating substrate, a gate metal layer where the above-describedscanning lines 28, the common electrode wirings 26 a, 26 b and the thinfilm transistor 30 are formed, a first interlayer insulating film formedthereon, a second metal layer formed over the first interlayerinsulating film, on which the data line 24 and the source electrode 30 band the drain electrode 30 a of the thin film transistor 30 are formed,and a second interlayer insulating film formed on the second metallayer. Further, the lower substrate 1 comprises an alignment film on theliquid crystal layer side.

The common electrodes 26 (26A, 26B) and the pixel electrodes 27 (27A,27B) are all formed in pectinate shapes as shown in FIG. 1, and eachtooth in the respective electrodes is extended in parallel to the dataline 24. Further, the teeth of the interdigital common electrode 26 andthe pixel electrode 27 are arranged alternately.

Reference numeral 26A indicates the reflective part common electrode,and reference numeral 26B indicates the transmissive part commonelectrode. Further, reference numeral 27A indicates the reflective partpixel electrode, and reference numeral 27B indicates the transmissivepart pixel electrode (see FIG. 1).

Each of the transmissive area T and the reflective area H describedabove in the liquid crystal display apparatus 101 employs the in-planeswitching system. In the liquid crystal display apparatus 101, electricfields in parallel to the above-described transparent insulatingsubstrate are generated between the common electrodes 26 (26A, 26B) andthe pixel electrodes 27 (27A, 27B). The alignment direction of theliquid crystal molecules is rotated within a plane in parallel to thetransparent insulating substrates 22 a, 22 b in accordance with thegenerated electric fields so as to perform a prescribed display. Thecommon electrodes 26 (26A, 26B) and the pixel electrodes 27 (27A, 27B)are pixels to which the data signals (selected by the scanning signalssupplied through the scanning lines 28, and supplied through the datalines 24) are written.

<Reflective Part (Reflection Area) H>

In the reflective area H, a base uneven film (uneven OC) 4 as a basefilm for forming the unevenness on the reflective plate is formed on thesecond interlayer insulating film (not shown) of the transparentinsulating film on the lower substrate 1 side in a thickness of about2.0 μm in average of the uneven parts, and a difference in heights ofabout 0.7 μm is provided to form the unevenness. On the base uneven film4, a reflective plate (uneven reflective plate) 99 of about 0.1-0.4 μmis formed. Furthermore, a flattening film 5 is formed on the reflectiveplate 99 as in FIG. 2 in a thickness of about 2.0-2.5 μm using acryl orthe like (see FIG. 2 and FIG. 3B).

Moreover, the reflective part pixel electrode 27A and the reflectivepart common electrode 26A are formed in a pectinate shape on theflattening film 5. The reflective part pixel electrode 27A is connectedto the source electrode 30 b of the TFT via a contact hole 39 a, and thereflective part common electrode 26A is connected to the above-describedcommon electrode wiring 26 a via a contact hole 39 b (see FIG. 1).

<Transmissive Part (Transmissive Area) T>

Meanwhile, in the transmissive area T, the flattening film 5 in commonto the reflective area H is formed (see FIG. 2) on the above-describedsecond interlayer insulating film (not shown), and the interdigitaltransmissive part pixel electrode 27B and transmissive part commonelectrode 26B are formed thereon (see FIG. 3A). The pixel electrode 27Band the common electrode 26B may be formed in common with theabove-described reflective area H and extendedly provided therefrom. Thepixel electrode 27B is connected individually to the source electrode 30b of the TFT via a contact hole 39 c, and the transmissive part commonelectrode 26B is connected to the common electrode wiring 26 b via acontact hole 39 d (see FIG. 1).

The lower substrate 1 and the counter substrate 2 comprise an alignmentfilm provided thereon, respectively, on the liquid crystal layer 3 side.Then, as shown in the drawing, rubbing processing is applied towards aprescribed direction tilted by about 10-30 degrees from the extendingdirection of the pixel electrodes 27A, 27B and the common electrodes26A, 26B so that the liquid crystal layer is aligned homogeneously.Thereafter, both substrates are laminated to face each other. This angleis called an initial alignment direction of the liquid crystalmolecules.

Further, a spacer (not shown) is provided between the lower substrate 1and the counter substrate 2 for keeping the thickness of the liquidcrystal layer 3. Further, a seal (not shown) is formed in the peripheryof the liquid crystal layer 3 for not leaking the liquid crystalmolecules to the outside. In the above-described liquid crystal layer 3,electric field drive (liquid crystal display) by the in-plane switchingdrive is executed with the electric fields applied between theinterdigital common electrodes 26A, 26B and pixel electrodes 27A, 27Bprovided by corresponding thereto as described above.

<Relation Between Angle of Incident/Exit Light with Respect to LiquidCrystal and Tilt Angle of Uneven Reflective Plate>

Now, there will be described the relation regarding angles of theincident/exit light to/from the liquid crystal 3 side and the tile angleof the uneven reflective plate 99 according to the embodiment.

FIG. 4 shows the relative relation between the incident angle θ₁/exitangle θ₄ and the tilt angle φ_(H) of the uneven reflective plate 99.

The tilt angle φ_(H) of the uneven reflective plate 99 is calculated bythe following expressions.

n₁ sin θ₁=n₂ sin θ₂   (1)

θ₃=θ₂φ_(H)   (2)

n₁ sin θ₄=n₂ sin θ₃   (3)

It is noted here that n₁=1.0 and n₂=1.6. In the above-describedconventional technique shown in FIG. 10, the uneven reflective plate 9is formed such that the light making incident at an incident angle (θ₁)of 15 degrees is reflected diffusely in the direction at an exit angle(θ₄) of 0 degree. However, in the case where the in-plane switchingdrive is employed to the reflective area (uneven reflective plate 99) asdescribed in the embodiment, there is required the uneven reflectiveplate 99 which has such a tilt angle φ_(H) that the light makingincident at the incident angle (θ₁) of 30 degrees is reflected diffuselyin the direction at the exit angle (θ₄) of 0-10 degrees, in order toachieve wide view angles in the reflection mode.

As shown in FIG. 5A and FIG. 5B, the tilt angle φ_(H) is an angle formedbetween the lower substrate 1 and a tangent from an arbitrary point onthe uneven reflective plate 99 or a tangent on an arbitrary point on thesurface 5A of the flattening film 5.

Further, as shown in FIG. 4, the tilt angle φ_(H) of the unevenreflective plate 99 is about 2-5 degrees, when light makes incident fromthe direction at the incident angle (θ₁) of 15 degrees and the reflectedlight is diffused in the direction of 0-10 degrees. Furthermore, thetilt angle φ_(H) of the uneven reflective plate 99 is about 6-9 degrees,when light makes incident from the direction at the incident angle (θ₁)of 30 degrees and the reflected light is diffused in the direction of0-10 degrees.

In this case, the tilt angle φ_(H) of the uneven reflective plate 99 forachieving the wide view angles may be set larger than the tilt angle ofthe conventional uneven reflective plate 9. With this, the unevenreflective plate 99 having a diffusive reflecting function can be set.In this case, on an experiment, it is confirmed that there is apossibility of having diffusive reflection even when the tilt angleφ_(H) of the uneven part of the uneven reflective plate 99 is within therange of 3-12 degrees.

It is difficult to form the uneven reflective plate 99 in such a mannerthat the entire tilt faces of each uneven part are constituted to have acertain tilt angle φ_(H). Therefore, the embodiment herein considers thetilt angle φ_(H) of the uneven reflective plate 99 as an average tiltangle of the entire tilt faces of each uneven part of the unevenreflective plate 99.

When executing the in-plane switching mode by the use of the in-planeswitching drive, the flattening film 5 is required on the unevenreflective plate 99 in order to form the interdigital thin electrode(for example, the reflective part pixel electrode 27A) in the reflectivearea H. Average tilt angle φ_(M) of the surface of the flattening film 5(see FIG. 5B) can be made smaller (close to flat state) than the tiltangle φ_(H) of the uneven reflective plate 99 by increasing thethickness of the flattening film 5.

The graph of FIG. 5C shows the state of changes in the thickness of theflattening film 5 and the average tile angle φ_(m) of the flatteningfilm surface, when the average tilt angle φ_(H) of the uneven reflectiveplate 99 is 6 degrees.

In an experimental example where the width of the interdigital electrodewas set as 3 μm, the interdigital electrode was formed when the averagetilt angle (φ_(M)) of the flattening film surface was 2.5 degrees orless, i.e. when the thickness of the flattening film 5 was 1.5 μm ormore. However, when the thickness of the flattening film was smallerthan 1.5 μm, exfoliation of the electrodes was observed.

Furthermore, when the width of the interdigital electrode was set as 1.5μm for the same experiment, the interdigital electrode was formed whenthe average tilt angle (φ_(M)) of the flattening film surface was 1.5degrees or less, i.e. when the thickness of the flattening film 5 was2.5 μm or more. However, when the thickness of the flattening film wassmaller than 2.5 μm, exfoliation of the electrodes was observed.Therefore, attaching/forming the interdigital electrodes can be expectedeven when the average tile angle φ_(M) of the flattening film surface iswithin the range of 1.5-2.5 degrees. It is preferable, however, for theaverage tile angle φ_(M) to satisfy φ_(M)≦1.5 degrees (within theconfirmed range) for securely forming the electrodes.

For the above-described flattening film 5, the one with the extremelysmall refractive index anisotropy Δn, e.g. the one with Δn≦0.001, wasused. For the refractive index anisotropy Δn, the smaller, the better.

By providing the flattening film 5 on the uneven reflective plate 99 inthis manner, the interdigital electrode can be formed. In addition, bysetting the surface that is in contact with the liquid crystal layer 3of the reflective area H to be flat or close to flat, it becomespossible to obtain such an advantage that the rotation drive within theplane of the liquid crystal by the in-plane switching drive can befurther stabilized at the same time.

Next, there will be described formation of the liquid crystal layers ofthe reflective part (reflective area) H and the transmissive part(transmissive area) T, in the case where the above-described unevenreflective plate 99 is applied to a transflective liquid crystal displayapparatus.

When it is assumed that the average tilt angle (φ_(H)) in the unevenpart of the uneven reflective plate 99 is 6 degrees and the pitch of theuneven parts is 20 μm, the difference in heights between the unevenparts is about 1 μm. The pitch of the uneven parts is the distancebetween the vertex of the convex part of the uneven reflective plate 99and the vertex of the neighboring convex part. The difference in heightsbetween the uneven parts is the difference between the vertex of theconvex part and the vertex of the neighboring concave part on eachsurface of the uneven reflective plate 99 or the flattening film 5 interms of the heights (see FIG. 2).

The shape of the above-described uneven reflective plate 99 is formed inaccordance with the surface shape of a base uneven film 4 (referred toas “uneven OC 4” hereinafter) as an organic film provided thereunder.When the lowest point of the uneven OC 4 surface reaches to the lowersubstrate 1, there is generated a flat part in the uneven reflectiveplate 99. Thus, the proportion of the incident light reflected regularlyfrom the uneven reflective plate 99 becomes increased. Therefore, thereflection property is deteriorated.

In order to avoid this, when the distance (a) between the lowest pointof the surface of the uneven OC 4 and the lower substrate 1 is set as1.5 μm (see FIG. 6A), for example, by considering the dispersions inproviding the difference in heights, the average film thickness (β) ofthe base uneven film (uneven OC 4) after forming the uneven reflectiveplate 99 becomes about 2.0 μm as shown in FIG. 6A.

In this case, since it is necessary to form the flattening film 5 withthe thickness of 2.5 μm on the uneven reflective plate 99 for formingthe interdigital electrode with the width of 1.5 μm, the film thickness(γ) after forming the flattening film 5 becomes 4.5 μm. This filmthickness becomes the difference in heights between the reflective partH and the transmissive part T in the pixel (see FIG. 6A).

Assuming now that a liquid crystal material with Δn=0.07 is used. Then,thickness of the liquid crystal layer 3 of the reflective part H havingΔnd of 137.5 nm (λ/4) becomes about 2 μm.

When this value is employed for the thickness of the liquid crystallayer 3 of the reflective part H described above, the liquid crystallayer 3 of the transmissive part T becomes 6.5 μm, including thedifference in heights between the reflective part H and the transmissivepart T. Thus, the thickness of the liquid crystal layer 3 corresponds toΔnd=455 nm, which is larger than Δnd=275 of the liquid crystal layer ofa λ/2 plate.

That is, as shown in FIG. 6B, the intensity of transmission light isproportional to sin²(πΔnd/λ), so that when Δnd of the liquid crystallayer 3 of the transmissive part T is shifted from a proper value, theintensity of transmission light becomes small, thereby deteriorating thecontrast.

Thus, by continuously forming the flattening film 5 provided on theuneven reflective plate 99 also on the transmissive part T, thedifference in heights between the reflective part H and the transmissivepart T becomes 2 μm, the liquid crystal layer 3 of the transmissive partT becomes 4 μm, and Δnd becomes 280 nm. With this, the thickness of theliquid crystal layer 3 of the transmissive part T becomes almost theoptimum value (see FIG. 7).

When the difference in heights on the surface of the flattening film 5on the uneven reflective plate 99 is to be eliminated completely, thethickness of the flattening film 5 becomes extremely thicker than theaverage film thickness (β) of the uneven OC 4. Thus, the difference inheights between the reflective part H and the transmissive part Tbecomes still smaller than the proper value, by applying the flatteningfilm 5 on the transmissive part T. Alternatively, it is possible thatthere is no difference in heights formed thereon.

In such a case, it is possible to obtain a proper difference in heightsby eliminating the flattening film 5 of the transmissive part T by theuse of half-exposure. However, it is not preferable in terms of themanufacturing efficiency, since a step therefor needs to be added.

Thus, it is not essential for the surface of the flattening film 5 to becompletely flat, as long as a proper difference can be obtained betweenthe heights of the transmissive part T and the reflective part H. Forexample, when the width of the interdigital electrode is 3 μm, there maybe formed difference in heights of uneven parts with an average tiltangle (φ_(M)) of 2.5 degrees on the surface. Meanwhile, when the widthof the interdigital electrode is 1.5 μm, there may be formed differencein heights of uneven parts with an average tilt angle (φ_(M)) of 1.5degrees or less on the surface.

It has already been described to form the flattening film 5 uniformly onthe transmissive part T and the reflective part H so as to provide thedifference in heights between the transmissive part and the reflectivepart H. In that case, the flattening film 5 is additionally applied tothe transmissive part T, compared to the conventional case describedabove. In the structure of FIG. 7, when Δn of the flattening film 5 is0.1, Δnd of the transmissive part T is changed by 250 nm because“2500×0.1=250”. When this Δnd is shifted from a proper value, theintensity of the transmission light becomes weak, as shown in FIG. 6B.However, if Δn of the flattening film 5 is extremely small (for example,about 0.001), the change in Δnd can be suppressed to 2.5 nm. Thus, thereis almost no change generated in the intensity of the transmissionlight, so that deterioration in the contrast can be avoided. Therefore,it is better for Δn of the flattening film 5 to be smaller.

Another Embodiment

FIG. 8-FIG. 9 illustrate another embodiment.

This embodiment illustrates the case where the uneven reflective plate99 and the flattening film 5 associated therewith according to theabove-described embodiment are applied to an FFS mode liquid crystaldisplay apparatus.

As shown in FIG. 8-FIG. 9, the FFS mode liquid crystal display apparatusis peculiar in respect that an uneven reflective plate 99H formedequivalently with the above-described uneven reflective plate 99 is alsoused as a reflective part common electrode 56A (i.e. common electrode56), and a transmissive part common electrode 56B is loaded closely tothe base substrate 1 described above.

That is, the common electrode and the pixel electrode are not mounted onthe same layer in the FFS mode liquid crystal display apparatus. In anycases, the transmissive part common electrode 56B and the unevenreflective plate 99H that also functions as the reflective part commonelectrode 56A are provided, respectively, on the base substrate 1 sidethrough the flattening film 5 as shown in FIG. 8 and FIGS. 9A, 9B. Otherstructures and the effects are the same as those of the above-describedembodiment.

In this way, it is also possible to obtain a liquid crystal displayapparatus that functions as the one obtained in the case of theembodiment described by referring to FIG. 1-FIG. 7.

With each of the embodiment as described above, the followings can befound as a result of trying out the various kinds of experiments asdescribed above.

That is, in a transflective liquid crystal display apparatus where boththe transmissive part (transmissive area) T and the reflective part(reflective area) H employ the in-plane switching drive, it becomespossible to diffusely reflect the light from the direction at theincident angle of 30 degrees in wide view angles in the directions atthe exit angles of 0-10 degrees, through setting the tilt angle of theuneven reflective plate 99 or 99H at 3-12 degrees (preferably 6-9degrees). Further, the flattening film 5 is provided on the unevenreflective plate 99 or 99H to make the top face of the layer on whichthe electrodes are formed to be flat or close to flat, so that thedriving electrodes can be stably attached/formed. With this, the stableoperation and the improved durability of the entire apparatus can beachieved.

Further, since the flattening film 5 is provided not only on thereflective part (reflective area) H but also on the transmissive part(transmissive area) T, Δnd of the liquid crystal layer 3 of thereflective part H and that of the transmissive part T can be set as λ/4and λ/2, respectively. With this, adverse influences for the display,which are generated by the differences in the optical properties of thetransmissive part T and the reflective part H, can be eliminatedeffectively in advance.

In short, the above-described embodiments can achieve the followings.

-   1) In a transflective liquid crystal display apparatus where both    the transmissive part and the reflective part employ the in-plane    switching drive, the average tilt angle of the uneven part of the    uneven reflective plate 99, 99H is set at 6-9 degrees. Therefore, it    becomes possible to diffusely reflect the light from the direction    at the incident angle of 30 degrees in the direction at the exit    angles of 0-10 degrees.-   2) The flattening film 5 is provided on the uneven reflective plate    99, 99H to make the top face of the layer on which the electrodes    are formed to be flat or close to flat. Therefore, the electrodes    can be stably formed.-   3) Further, since the flattening film is provided also on the    transmissive part, Δnd of the liquid crystal layer of the reflective    part and that of the transmissive part can be set as λ/4 and λ/2,    respectively. As a result, it becomes possible to provide a    transflective liquid crystal display apparatus that is highly    reliable and stable in operation in this respect.

The above-described structure is not applied limitedly to the opticallayout and the drive method of the above-described liquid crystaldisplay apparatuses. It can be applied generally to the transflectiveliquid crystal display apparatuses that employ the in-plane switchingdrive.

1. A transflactive liquid crystal display apparatus, comprising: areflective area and a transmissive area; an uneven reflective plateprovided in the reflective area and electrically connected to commonelectrodes; a flattening film laminated on the uneven reflective plate;and pixel electrodes arranged on the flattening film, wherein the unevenreflective plate comprises a diffusive reflecting function thatdiffusely reflects light making incident at an incident angle of 30degrees towards directions at exit angles of 0-10 degrees, and a surfaceof the flattening film is set to be substantially flat.
 2. Thetransflective liquid crystal display apparatus as claimed in claim I,wherein an average tilt angle of the uneven reflective plate is set as3-12 degrees, and an average tilt angle of the surface or the flatteningfilm is set to a value not exceeding a range of 3-5 degrees.
 3. Thetransflective liquid crystal display apparatus as claimed in claim 1,wherein an average tilt angle of the uneven reflective plate is set as6-9 degrees, and an average tilt angle of the surface of the flatteningfilm is set to a value not exceeding a range of 3-5 degrees.
 4. Thetransflective liquid crystal display apparatus as claimed in claim I,wherein the uneven reflective plate has a difference of 0.6 μm or morein heights of uneven parts, and a difference in heights on the surfaceof tile flattening film is 0.4 μm or less.
 5. A transflective liquidcrystal display apparatus as claimed in claim 1, wherein: Δnd of aliquid crystal layer of the reflective area is set as about λ/4, and Δndof a liquid crystal layer of the transmissive area is set as about λ/2;and the flattening film is formed uniformly from the reflective area tothe transmissive area continuously.
 6. A transflective liquid crystaldisplay apparatus as claimed in claim 1, wherein reflective indexanisotropy Δn of the flattening film is set as 0.001 or less.